1. Field of the Invention
The present invention relates to a sheet feeding apparatus to be used in a sheet handling machine such as a copying machine and arranged to feed a document or a paper sheet on which an image is to be transferred.
2. Description of Related Arts
In an image reading apparatus or an image forming apparatus such as a copying machine, a printer, an image reader, a facsimile or the like, there is used a sheet feeding apparatus for automatically feeding a sheet such as a document, recording paper or the like.
FIG. 5 is a section view illustrating the arrangement of a portion of a document feeding apparatus to be used for feeding a document to the document reading unit of a digital electrostatic copying machine. In the vicinity of and on the tip of a document placing unit 31 on which a plurality of documents can be placed in lamination, there is disposed a preliminary feeding roller 32 for taking a document from the document placing unit 31. Downstream of the preliminary feeding roller 32 in the document transfer direction (leftward in FIG. 5), a feeding roller 33 and a separating roller 34 are disposed opposite to each other with a sheet feeding passage 35 interposed therebetween.
The feeding roller 33 has a support shaft 33a to which a lever 36 is rotatably attached. The lever 36 has a rocking end to which a support shaft 32a of the preliminary feeding roller 32 is rotatably attached. Provision is made such that a rotational force is given to the feeding roller 33 from a drive motor (not shown) and that this rotational force is also transmitted to the preliminary feeding roller 32 through a gear mechanism (not shown).
Provision is made such that the rotation of the support shaft 33a of the feeding roller 33 is transmitted to the lever 36 through a one-way clutch. The one-way clutch transmits, to the lever 36, only the rotation of the feeding roller 33 in the anti-sheet feeding direction (counterclockwise in FIG. 5). Accordingly, when the feeding roller 33 is rotated at a predetermined angle in the anti-sheet feeding direction, the lever 36 is rotated counterclockwise, enabling the preliminary feeding roller 32 to be raised. When the preliminary feeding roller 32 is thus raised, a sheet feeding port 37 serving as the inlet of the sheet feeding passage 35 is widely opened, enabling a document D to be readily set.
Disposed between the preliminary feeding roller 32 and the feeding roller 33 is a document stopper 38 for preventing one or more documents D from being inserted to the position of the feeding roller 33 when setting documents D. This document stopper 38 is made of a plate-like body so disposed as to be able to rock around the upper end thereof. A locking mechanism 40 for locking the rocking of the document stopper 38 is disposed in association therewith. This locking mechanism 40 has drive means such as a solenoid or the like for locking the document stopper 38 and for releasing the locked state thereof.
When the solenoid is energized, the document stopper 38 can rock, allowing the document D to be transferred to the feeding roller 33. While the solenoid is not energized, the document stopper 38 is locked by the locking mechanism 40. In such a state, even though a document D is placed on the document placing unit 31 such that the document D is inserted into the position of the sheet feeding port 37, the tip of the document D is regulated by the tip 38a of the document stopper 38, preventing the document D from reaching the feeding roller 33.
When setting documents by the user, the preliminary feeding roller 32 is raised and the document stopper 38 is locked. This prevents documents from reaching the feeding roller 33, thus preventing defective separation of documents.
If documents are manually inserted into the sheet feeding passage 35 across the feeding roller 33 and the separating roller 34 and the tips of the documents reach a roller further downstream of the separating roller 34 in the sheet feeding passage 35, the documents can no longer be separated one by one under the action of the separating roller 34. The document stopper 38 prevents the occurrence of such a phenomenon.
When the locked state of the document stopper 38 is released, a document can enter into the sheet feeding passage 35 while the document stopper 38 is rocked by the document.
To intercept the document transfer by the document stopper 38 and to release such an interception, this document feeding apparatus requires, in addition to a drive motor for driving the support shaft 33a of the feeding roller 33, locked-state releasing means such as a solenoid or the like for releasing the transfer interception by the document stopper 38. There is further required an electric system for electrical supply to the drive source. This complicates the apparatus in arrangement and increases the number of component elements thereof.
In the document feeding apparatus of the prior art, since the preliminary feeding roller 32 is raised to a predetermined position, a rated electric current is given to the drive motor, causing the same to supply a relatively great torque. However, if an unforeseen accident occurs such that the drive motor does not stop even after the preliminary feeding roller 32 has been raised to the predetermined position, the preliminary feeding roller 32 and the lever 36 are still continuously raised and ultimately come in contact with a cover C of the apparatus. If such a state continues, a great force is continuously exerted to the cover C and the one-way clutch disposed in association with the lever 36. This involves the likelihood that component elements of the apparatus are damaged.